Question

The partial pressures (in mm Hg) of oxygen (O₂) and carbon dioxide (CO₂) at alveoli (the site of diffusion) are:

• A. pO₂ = 159 and pCO = 0.3
• B. pO₂ = 104 and pCO₂ = 40
• C. pO₂ = 40 and pCO₂ = 45
• D. pO₂ = 95 and pCO₂ = 40

Answer 1

The correct option is B

pO₂ = 104 and pCO₂ = 40

The correct option is B.

Explanation for the correct option:

1. Partial pressure is the amount of pressure that each gas in a mixture exerts. Gas will flow from one area with greater partial pressure to another with lower partial pressure.
2. When compared to the partial pressure of carbon dioxide (p CO₂) (40 mm of Hg), the partial pressure of oxygen (pO₂) in alveolar air is greater (104 mm of Hg).
3. Deoxygenated blood has a lower partial pressure of oxygen (40 mm of Hg) than it does of carbon dioxide (45 mm of Hg).
4. The oxygen diffuses from the alveoli into the blood capillaries as a result of the difference in oxygen partial pressures between alveolar air and deoxygenated blood

Final answer: The partial pressures (in mm Hg) of oxygen (O₂) and carbon dioxide (CO₂) at alveoli (the site of diffusion) are pO₂ = 104 and pCO₂ = 40.